How to Use the Command 'fmt' (with Examples)

The fmt command is a versatile text formatting utility available on Unix-like operating systems. It is part of the GNU Core Utilities and is primarily used to reformat plain text. Its main purpose is to read a file and output the content with neatly arranged lines, the width of which can be configured. By default, fmt aims for lines up to 75 characters in length, providing uniformity and better readability in textual data. This utility is particularly useful in scripting and document processing tasks where consistent formatting is required.

Use Case 1: Reformat a File

Code:

fmt path/to/file

Motivation:

The most straightforward application of fmt is reformatting a text file to maintain line width consistency. Text editors often handle line breaks differently, making plain text appear jagged or uneven, especially when transferred across systems or applications. Here, fmt automatically adjusts the text, ensuring that each line doesn’t exceed the default 75-character limit, providing a tidy and professional appearance.

Explanation:

• fmt: This is the command itself, initiating the text reformatting process.
• path/to/file: This is a placeholder for the file path of the text file you wish to reformat. When executed, fmt will adjust line lengths up to its default width of 75 characters.

Example Output:

Consider a text file containing lengthy paragraphs with inconsistent line breaks. After running fmt, the text will be uniformly reformatted, with lines neatly wrapped to 75 characters or less.

Use Case 2: Reformat a File with Specified Width

Code:

fmt -w 50 path/to/file

Motivation:

Sometimes, the default line width is not suitable for every document or display requirement. For instance, if you are preparing text for a narrow column in a newsletter or a specific screen width, you might opt for a different width. Using the -w option customizes the line length, thereby better aligning the text with these particular requirements.

Explanation:

• fmt: This command kickstarts the reformatting.
• -w 50: The -w flag is used to specify a maximum line width. Here, 50 sets the line limit to 50 characters.
• path/to/file: As before, this indicates the file to be reformatted.

Example Output:

A document with irregular breaks will be reformatted with lines containing up to 50 characters, thus fitting perfectly into narrower layout spaces.

Use Case 3: Reformat Without Joining Short Lines

Code:

fmt -s path/to/file

Motivation:

In cases where a text file contains lines that are deliberately short for stylistic or structural reasons—such as poetry, code comments, or lists—you might want to maintain them as they are, while still reformatting longer lines. The -s option ensures that only longer paragraphs are modified, preserving the intended structure.

Explanation:

• fmt: Initiates the reformatting of the file.
• -s: Stands for “split” and prevents short lines from being joined together unnecessarily.
• path/to/file: The target file is indicated here.

Example Output:

Lines under a certain length will remain as they originally were, while longer ones will be adjusted to maintain consistent width.

Use Case 4: Reformat with Uniform Spacing

Code:

fmt -u path/to/file

Motivation:

Uniform spacing is often desired when making text legible and aesthetically pleasing. This is particularly important in documents where readability and presentation must be maintained, such as reports, where a single space between words and a double space between paragraphs is expected. The -u option refines a document’s spacing to meet these criteria.

Explanation:

• fmt: Calls upon the formatting utility.
• -u: Ensures that spacing is standardized, with one space between words and two between paragraphs.
• path/to/file: Represents the text file being processed.

Example Output:

Text initially plagued with erratic spacing will be converted into a document with uniform spacing, promoting readability.

Conclusion:

The fmt command is a powerful tool for ensuring uniformity in text formatting across various use cases. Whether adjusting line widths or preserving artistic short lines, its flexible set of options cater to diverse text processing needs. It makes the process of reformatting text efficient, ensuring that documents meet specific aesthetic or structural requirements without manual adjustments.